The present invention relates to the field of wired remote control circuits and, more particularly, to a circuit which will not reduce the supply voltage in the control unit.
In a system such as the radio receiver for an automobile, the customary arrangement includes an antenna on the exterior of the vehicle, a tuner and amplifier placed behind the dashboard and one or more loudspeakers placed as appropriate in the interior of the vehicle. By some individual standards for audio signals, the usual automobile radio does not supply enough audio power. Higher powered audio amplifiers and additional speakers have sometimes been added to provide this desired audio level. It is desirable to activate these expanded systems with the original radio controls, but most known systems have reduced the voltage supply to the original radio. Since many automobile radios are designed to operate optimally within a narrow range of supply voltages, any reduction in the A+ supply can produce severe effects on performance. One example of such a system is the use of a PN junction device in the DC supply lead of the control unit (receiver) to produce a detectable voltage drop when the control unit is activated, with the voltage drop creating a change in logic level in the control line. Another control system runs the DC supply for the control unit through a relay coil. Each of these produces an undesirably large voltage drop for the control unit supply.